How to add Principled volume as default
You could create a default smoke material and save it in your default Blender starting scene if you find yourself doing smoke sims really often. Or you could write a small python script that create a domain with the right material and node setup. At the end of the day it's just a few extra clicks, I wouldn't bother with it. Principled BSDF is just the default setup for all Blender materials (remember that materials are completely independent data from objects).